Deleted files:
* `user_preferences_camera_sound.dart`
* `user_preferences_crash_reporting.dart`
* `user_preferences_haptic_feedback.dart`
* `user_preferences_send_anonymous.dart`

New files:
* `user_preferences_item.dart`: Item for preferences, with labels for pre-filtering and widget builder.
* `user_preferences_search_page.dart`: Search page for preferences, with TextField filter.

Impacted files:
* `abstract_user_preferences.dart`: new `getLabels` method for filtering; children are now `UserPreferencesItem` for filtering; minor refactoring.
* `user_preferences_account.dart`: children are now `UserPreferencesItem`; minor refactoring
* `user_preferences_advanced_settings.dart`: added a static `UserPreferencesItem` getter
* `user_preferences_attribute_group.dart`: children are now `UserPreferencesItem`; minor refactoring
* `user_preferences_choose_accent_color.dart`: added a static `UserPreferencesItem` getter
* `user_preferences_choose_app_theme.dart`: added a static `UserPreferencesItem` getter
* `user_preferences_choose_text_color_contrast.dart`: added a static `UserPreferencesItem` getter
* `user_preferences_connect.dart`: children are now `UserPreferencesItem`; minor refactoring
* `user_preferences_contribute.dart`: children are now `UserPreferencesItem`; minor refactoring
* `user_preferences_country_selector.dart`: added a static `UserPreferencesItem` getter
* `user_preferences_dev_mode.dart`: children are now `UserPreferencesItem`; minor refactoring
* `user_preferences_faq.dart`: children are now `UserPreferencesItem`; minor refactoring
* `user_preferences_food.dart`: children are now `UserPreferencesItem`; minor refactoring
* `user_preferences_image_source.dart`: added a static `UserPreferencesItem` getter
* `user_preferences_language_selector.dart`: added a static `UserPreferencesItem` getter
* `user_preferences_page.dart`: moved `getUserPreferences` to `PreferencePageType`; minor refactoring
* `user_preferences_rate_us.dart`: added a static `UserPreferencesItem` getter
* `user_preferences_settings.dart`: children are now `UserPreferencesItem`; minor refactoring
* `user_preferences_share_with_friends.dart`: added a static `UserPreferencesItem` getter
* `user_preferences_widgets.dart`: new classes `UserPreferencesItemSwitch` and `UserPreferencesItemTile`

…e.dart